Management of Iatrogenic Nerve Injuries Flashcards
1
Q
spontaneous neurosensory recovery is______
A
unpredictable
2
Q
surgical nerve repair modalities have:
A
unpredictable outcomes
3
Q
what is key to preventing iatrogenic nerve injuries
A
case selection
4
Q
which nerves are of concern in dentistry
A
- inferior alveolar nerve (V3)
- mental nerve (V3)
- lingual nerve (V3)
- long buccal nerve (V3)
- maxillary nerve and branches (V2)
- facial nerve (VII)
5
Q
what nerves affect sensory function in dentistry
A
- inferior alveolar
- mental nerve
- lingual nerve
- long buccal nerve
- maxillary nerve and branches
6
Q
what nerves affect motor function
A
facial nerve
7
Q
the inferior alveolar nerve and its branches can potentially be injured during:
A
- extraction of lower third molars
- administration of local anesthetic injection
- during placement of endosseous dental implants, plates and screws
- during RCT
- due to pathology
- due to infections such as osteomyelitis
8
Q
what is the most common etiology for iatrogenic trauma of IA nerve
A
third molar extraction
9
Q
where is mandibular canal usually located
A
inferior and buccal to the impacted mandibular third molars
10
Q
what is the incidence of injury to the IA nerve with 3rd molar extraction
A
1.2% on average
11
Q
_____ of neurosensory disturbances of injury to IA nerve last more than 12 months
A
22%
12
Q
to prevent nerve injury of IA you should leave a _____ safety zone above nerve while placing implant
A
2mm
13
Q
remember that the dental implant osteotomy drills have ______ extra length for preparation of implant osteotomy site
A
1mm
14
Q
always consider __________ while placing the implants in the posterior mandible
A
anterior loop of the mental nerve
15
Q
if the dental implant is placed anterior to the mental foramen:
A
then the distal surface of the implant should be greater than 2mm mesial to the mental foramen
16
Q
what are the types of damage done by needle injury to the IA
A
intrafascicular vs extrafascicular
17
Q
which type of needle injury is the most harmful
A
intra- fascicular
18
Q
what does nerve damange to intrafascicular injection lead to
A
inflammation, neuropeptide production. changes in signal transduction in axon and cell body leading to chronic pain
19
Q
nerve injury during RCT is _______ a frequent complication
A
not
20
Q
is the incidence of nerve paresthesia after injection with higher concentration of LA higher or lower
A
higher
21
Q
nerve injury during RCT is usually due to:
A
over instrumentation, irritant irrigants and canal medicaments, and extruded sealants and obturation materials
22
Q
what does the lingual nerve do
A
- supplies sensory innervation to the anterior 2/3 of the tongue and lingual mucosa
- provides taste to anterior 2/3rd of tongue via chorda tympania (VII)
23
Q
what is the diameter of the lingual nerve
A
3.2mm
24
Q
the lingual nerve is also called_____ because:
A
the invisible nerve because you cannot locate this nerve on routine radiographs
25
how can injuries to the lingual nerve occur
- extraction of lower third molars
- placement of dental implants through lingual cortex
- pathology
- local anesthetic injection
26
what percentage in the lingual nerve above the lingual crest
14%
27
what percentage in the lingual nerve in the retromolar pad region
1%
28
what percentage in the lingual nerve in direct contact with the lingual plate
23%
29
what is the most common reason for iatrogenic trauma to the lingual nerve
third molar extraction
30
what is the average incidence of injury to the lingual nerve with 3rd molar extractions
0.9%
31
about ______ of the deficits from lingual nerve injury from third molar extractions are permanent
25%
32
what is parasthesia
an abnormal sensation. not necessarily unpleasant or painful
33
what is dysethesia
an unpleasant abnormal sensation
34
what is anesthesia
the absence of perception of stimulation by noxious or non-noxious stimuli
35
what is the epineurium
outer covering which forms a sheath around the nerve
36
what does the perineurium surround
nerve fibers, which are axons, organize into bundles known as fascicles with each fascicle surrounded by the perineurium
37
what is the endoneurium
between individial fibers is an inner layer of endoneurium
38
what is neurapraxia
-temporary interruption conduction
- a conduction block resulting from mild insult to nerve trunk
- temporary paralysis of a nerve caused by lack of blood flow or by pressure on the affected nerve with no loss of structural continuity
39
describe how long neurapraxia lasts
- there is no axonal degradation and sensory recovery is complete and occurs in a matter of hours to several days
- the sensory deficit is usually mild and characterized by paresthesia
40
what is axonotmesis
a more severe injury as compared to neurapraxia. afferent nerve fibers undergo degenderation but the nerve trunk is grossly intact
41
describe recovery of axonotmesis
- sensory recovery is good but incomplete
- the period of recovery is related to the rate of axonal regeneration and usually takes several months
- the sensory deficit is characterized by severe parasthesia
42
what is neuromesis
- neural tube is severed
- this is the most severe nerve inury where complete disruption of the nerve takes place
43
describe the recovery from neurotmesis
- the sensory deficit is characterized by anesthesia
- injuries are likely permanent without repair
44
describe the size, conduction velocity, and function of A alpha fibers
- 12-20
- 70-120
- position, fine touch
45
describe the size, conduction velocity, and function of A beta fibers
- 6-12
- 35-170
- proprioception
46
describe the size, conduction velocity, and function of A delta fibers
- 1-6
- 2.5-3.5
- superficial pain, temperature
47
describe the size, conduction velocity, and function of C fibers
-0.5-1
- 0.7-1.5
- deep pain, temperature
48
what is the scale for subjective assessment
- 1: complete absence of sensation
- 2: almost no sensation
- 3: reduced sensation
- 4: almost normal sensation
- 5: fully normal sensation
49
how do you map on a patient
the areas perceived by the patient as abnormal are mapped
50
what is the objective assessment
- level A: static two point discrimination, brush stroke directional discrimination (normally about 6mm)
- level B: contact detection
- level C: pinprick nocicpetion, thermal discrimination
51
what is the level A test - two point discrimination used for
to determine the response of the slowly adapting larger myelinated fibers (A alpha)
52
how is the level A test done for two point discrimination
- with an instrument with which the distance between the two points can be altered
- calipers can be used for this
- performed with the patients eye closed and with 2 points of the caliper essentially touching so that the patient is able to discriminate only one point
- the distance between the 2 points are increased in 2mm increments until the patient can discriminate between two distinct points at 6mm which is then considered normal
53
what is the brush stroke directional discrimination test used for
to determine the response of the slowly adapting larger myelinated fibers (A alpha and A beta myelinated axons)
- the sensory modalities for these receptors are vibration, touch and flutter
- assess the quantity and density of functional sensory receptors and afferent fibers
54
what are the level A tests
- two point discrimination
- brush stroke directional discrimination
55
how is the brush stroke directional discrimination test done
- this test can be performed with a fine sable or camel hair brush
- the brush is stroked gently across the area of involvement at a constant rate, and the patient is asked to indicate the direction of the movement and the correct number of patient statements out of 10 is recorded
56
describe the contact detection for level B tests
Von Frey Filaments
57
what are the Level C tests
- contact detection
- thermal discrimination
- pinprick nociception
58
what needle is used for pinprick nocioception
30 guage
59
what are the critical factors to consider when treating a nerve injury
- correct diagnosis/patient selection
- prompt evaluation of suspected nerve injuries
- type of injury
60
what is the prognosis and treatment for neurapraxia
- generally have a good prognosis
- generally no treatment is required except for periodic monitoring
61
what are the treatments for neurapraxia
- if a nerve is compressed by an implant or adjacent bone, the implant should be reverse torqued away from the nerve or removed
- in some cases methyl prednisone dose packs can be prescribed to the patient
62
what are the indications for surgery for nerve injuries
- intolerable anesthesia or hypoesthesia with no signs of recovery beyond 3 months
- witnessed severance of nerve
63
what are the contraindications for surgery
- tolerable anesthesia/hypoesthesia
- improvement on periodic objective testing
- greater than 6-12 months of time lapse from nerve injury
64
surgical treatment includes:
- surgical exploration of the nerve
- identification and removal of pathology if present
- identification and repair of severed nerve endings in a tension free manner (epineural neurorrhaphy)
65
describe surgical nerve repair
- nerve repair is completed under general anestheisa in an OR setting
- magnification using 3.5 X loupes or operating microscope with fiberoptic lighting
- repair using 8-0 nylon suture in epineural fashion
66
if tension free repair is not possible______ is mandatory
nerve grafting
67
what types of grafts are used
sural nerve (30mm) and greater auricular nerve (15mm) grafts
68
why is the sural nerve preferred
it most appropriately matches the nerve diameter and the fascicular number and pattern of the trigeminal nerve
69
what are the success rates with nerve grafting
25-90% but variable and unpredictable
70
empty nerve tubes can be effective in gaps _______ however reliability diminishes in gaps above _____
5mm;5mm
71
describe decullularized nerve allograft
- harvested from cadavers
- decellularized with detergents
- graft sterilized with gamma radiation
72
the 3D archicetrue of decellularized nerve grafts are inherent to the nerve is maintained to provide structural support for:
regenerating axons
73
what is the timeline for the decellularized nerve allograft
- hours: provides 3D scaffolding to support the body's own regeneration process
- days: clean and clear pathways allow cell migration and axonal regneration
- months: axon regeneration is well distributed throughout cross section
- years: incorporated into the patients own tissue
74
what are the types of grafts available for nerve repair
- nerve autograft
- avance nerve graft
- hollow tube
75
